1. Field of the Invention
The invention generally relates to the field of ultrasonic detectors and, more particularly, to a system using ultrasonic detectors to monitor leaks of compressed gas.
2. Description of the Related Art
It is well known that ultrasonic generators and detectors can be used to locate leaks or defects, e.g., in pipes. Such a system is shown in U.S. Pat. No. 3,978,915 to Harris. In that arrangement, ultrasonic generators are positioned in a chamber through which the pipes pass. At the ends of these pipes, exterior to the chamber, ultrasonic detectors are located. At the point where a leak occurs in the pipe or the pipe wall is thin, the ultrasonic energy will enter the pipe from the chamber and travel to the end of the pipe where the detector is located. The detector will receive an ultrasonic signal at the end of the pipe indicating the existence of the leak or weak spot in the pipe.
Since ultrasonic energy used for these purposes is generally in the range of 40 kHz, it is too high in frequency to be heard by a human being. Thus, means are typically provided for heterodyning, or frequency shifting, the detected signal into the audio range, and various schemes are available for doing this.
When using ultrasonic energy to detect leaks, it is useful to have an ultrasonic detector which indicates the presence and intensity of ultrasonic energy both visually and audibly. U.S. Pat. No. Re. 33,977 to Goodman et al. discloses an ultrasonic sensor that displays the intensity of the detected signal on an output meter operable in either linear or logarithmic mode, and also provides for audio output through headphones. U.S. Pat. No. 4,987,769 to Peacock et al. discloses an ultrasonic detector that displays the amplitude of the detected ultrasonic signal on a ten-stage logarithmic LED display. However, the detector disclosed in Peacock does not process the detected signal to produce an audible response, nor does it provide for signal attenuation after the initial pre-amplification stage.
Whenever there is a leak of compressed gas, it typically must be made up by generating more compressed gas in order to keep the relevant industrial process operating correctly. Knowing the operating parameters of the compressor used to generate the compressed gas, it is possible to calculate the amount of electricity that is needed for this purpose, and hence the amount of electrical energy that is wasted as a result of the leak.
When compressors are located throughout a large industrial site, it is most common to have personnel walk throughout the plant with a battery powered handheld detector making readings and storing the dB value and the location of the measurement in the detector. They return to a central location were the information is downloaded to a computer. However, it is disclosed in applicants' U.S. Pat. No. 11/339,811 filed on Jan. 24, 2006 to monitor the compressors by remote ultrasonic detectors, whose outputs are fed back by wire or wirelessly to a common monitoring location. Thus, the site operator can dispatch a repair crew to locations were the detectors indicate a leak is occurring. However, it may not be cost efficient to dispatch a repair crew to fix every leak. Depending on its size, the value of the electricity needed to compensate for the leak may be much smaller than the cost of the repair crew. In such a case, the leak may be noted for repair during routine maintenance or during a repair mission in the area for some other reason.
Making the decision about whether it is cost effective to send an immediate repair crew can be difficult and time consuming itself Thus, a detector which provides an output in terms of energy loss would be valuable to the site operator, not only in determining the effect of a single compressed gas leak, but in determining the cost of multiple leaks throughout the site.
With the recent acceptance of global climate change as a result of carbon dioxide emissions, various proposals have been made as to how industrial sites are to be monitored for their effect on the environment. One such proposal envisioned by the Kyoto Protocol involves the determination of the carbon footprint of an enterprise (i.e., a measure of the amount of carbon dioxide (CO2) and other greenhouse gases emitted by the enterprise, the setting of a limit on the footprint, and the possibility of trading carbon credits between enterprises that are below their carbon footprint with those which are above, so that an acceptable average is reached.
The generation of electricity to drive a compressor to replace leaking compressed gas results in an increase in carbon dioxide in the air, assuming the electricity is generated by carbon based fuels such as coal or oil, as opposed to nuclear energy. Thus, a relevant consideration for a site operator receiving information about a compressed gas leak is not only whether the cost to repair it exceeds the cost for the electricity to replace it, but whether this additional electricity would put the site close to exceeding its allowable carbon footprint. As with the calculation of the electrical energy loss by the leak, the carbon footprint effect can be very difficult for a site operate to determine.